Optical semiconductor parts such as LED have many advantages including small size, efficiency, vivid color emission, elimination of bulb failure, excellent drive characteristics, resistance to vibration, and resistance to repeated turn-on and off. These parts are thus often utilized as various indicators and light sources. Optoelectronic devices using optical semiconductor parts are mounted on substrates, which are now typically made of polyphthalamide (PPA) resins.
The current rapid advance of the optoelectronic technology has brought about photo-semiconductor devices of increased output and shorter wavelength. Photo-semiconductor devices are often encapsulated or mounted using prior art PPA resins as colorless or white material. However, these encapsulants and substrates are substantially degraded during long-term service and susceptible to visible color shading, separation and a lowering of mechanical strength. It is desired to overcome these problems effectively.
More particularly, JP 2656336 discloses that an optoelectronic device is encapsulated with a B-staged epoxy resin composition, in the cured state, comprising an epoxy resin, a curing agent, and a curing promoter, the components being uniformly mixed on a molecular level. As to the epoxy resin, it is described that bisphenol A epoxy resins or bisphenol F epoxy resins are mainly used although triglycidyl isocyanate and the like may also be used. In examples, a minor amount of triglycidyl isocyanate is added to the bisphenol A or F epoxy resin. The present inventors have empirically found that this B-staged epoxy resin composition for semiconductor encapsulation tends to yellow when held at high temperatures for a long period of time.
Triazine derivative epoxy resins are used in LED-encapsulating epoxy resin compositions as disclosed in JP-A 2000-196151, JP-A 2003-224305, and JP-A 2005-306952. None of these patents succeed in solving the problem of yellowing during long-term service at high temperature.
JP-A 2006-077234 describes a LED-encapsulating resin composition comprising an organopolysiloxane having a weight average molecular weight of at least 5×103 and a condensation catalyst. Since this organopolysiloxane must be transparent and liquid at room temperature, the composition does not lend itself to transfer molding and compression molding.
Citation List
Patent Document 1: JP 2656336
Patent Document 2: JP-A 2000-196151
Patent Document 3: JP-A 2003-224305
Patent Document 4: JP-A 2005-306952
Patent Document 5: JP-A 2006-077234